With development of the LIE (Long Term Evolution, Long Term Evolution) technology, CA (Carrier Aggregation, carrier aggregation) is introduced into the existing LTE system, where resources of multiple CCs (Component Carriers, component carriers) may be simultaneously scheduled for a UE (User Equipment, user equipment) to use, so as to provide higher peak rates and fulfill higher service requirements. For PDCCH (Physical Downlink Control Channel, physical downlink control channel) transmission in a CA system, one practice is to encode control information of multiple carriers independently to generate multiple independent PDCCHs; and another practice is to encode control information of multiple carriers jointly, that is, multiple carriers are scheduled by using a joint PDCCH, where the joint coding may reduce signaling overhead of the PDCCH by sharing certain control information between carriers. For example, a jointly coded PDCCH requires only a 16-bit CRC (Cyclical Redundancy Check, cyclic redundancy check).
In the prior art, carriers are mostly scheduled by means of joint coding. Specifically, a base station configures N carriers for a terminal, where N is a natural number greater than 1; the terminal and the base station each determine a DCI format set according to transmission mode information of the N carriers configured by the base station, where the DCI format set includes multiple DCI formats, the PDCCH corresponding to each DCI format carries scheduling information of N carriers. In addition, search space is determined according to a candidate format set. The base station transmits a PDCCH in the search space, and the terminal receives the PDCCH also in the search space.
After analyzing the prior art, the inventor finds that the prior art has at least the following disadvantages: where joint coding is applied, if the UE reserves a payload size for all carriers configured for the UE but the base station schedules only one carrier or only a part of the carriers to the UE at a time point, the UE may fill the PDCCH with null bits for the scheduling information corresponding to unscheduled carriers, which leads to waste of overhead.